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| United States Patent |
5,137,760
|
|
Lundquist
|
August 11, 1992
|
Deacidification process
Abstract
This invention relates to a process for treating a printed cellulosic
article for inhibiting acid promoted deterioration thereof comprising
providing in a pressure vessel containing said article, a transport medium
containing carbon dioxide, and base material dispersed in said medium for
transport to said article said vessel being pressurized with said carbon
dioxide to between about 650 and about 1200 psi and maintained for a
sufficient treatment period to cause substantial pervasion of said base
material in said article, and separating said medium from said article.
| Inventors:
|
Lundquist; Eric G. (Hillsborough, CA)
|
| Assignee:
|
Document Reprocessors (San Francisco, CA)
|
| Appl. No.:
|
696594 |
| Filed:
|
May 7, 1991 |
| Current U.S. Class: |
427/439; 422/40; 427/296; 427/377 |
| Intern'l Class: |
B05D 001/18 |
| Field of Search: |
427/296,439,377
422/40
|
References Cited
U.S. Patent Documents
| 3676182 | Jul., 1972 | Smith | 427/421.
|
| 4318963 | Mar., 1982 | Smith | 427/296.
|
Primary Examiner: Lusignan; Michael
Attorney, Agent or Firm: Shoemaker and Mattare, Ltd.
Parent Case Text
This is a continuation of application Ser. No. 07/335,366, filed Apr. 10,
1989, now abandoned.
Claims
I claim:
1. The process for treating a printed cellulosic article for inhibiting
acid promoted deterioration thereof, comprising providing in a pressure
vessel containing said article, a transport medium containing carbon
dioxide, and base material dispersed in said medium for transport to said
article, said vessel being pressurized with said carbon dioxide to between
about 650 and about 1200 psi and maintained for a sufficient treatment
period to cause substantial pervasion of said base material in said
article, and separating said medium from said article.
2. The process of claim 1 wherein the temperature of said medium is
maintained between about 0.degree. C. and about 40.degree. C.
3. The process of claim 2 wherein the temperature of said medium is
maintained below about 31.0.degree. C. and the pressure is maintained
above about 650 psi.
4. The process of claim 3 wherein the base material is selected from
inorganic and organic salts, oxides, alkoxides or hydroxides of magnesium,
alkaline earth metals or alkali metals, or mixtures or complexes thereof.
5. The process of claim 1 wherein the concentration of base material cation
in said transport medium ranges between about 5.0 and about 0.01% by
weight
6. The process of claim 1 wherein cosolvent is admixed with said carbon
dioxide in a liquid volumetric ratio of CO.sub.2 /cosolvent of from about
20/1 to about 1/3.
7. The process of claim 4 wherein the base material is substantially
insoluble in liquid carbon dioxide and is dispersed therein by agitation.
8. The process of claim 7 wherein the agitation is effected by turbulent
carbon dioxide flow.
9. The process of claim 6 wherein the cosolvent is selected from alcohols,
hydrocarbons, halogenated hydrocarbons, or mixture thereof.
10. The process of claim 6 wherein at least one of the cosolvents is
halogenated hydrocarbon.
11. The process of claim 3 wherein the base material is converted in situ
to a carbonate which, in aqueous system, gives a basic pH.
12. The process of claim 1 wherein said vessel and article are flushed
during or after said treatment period with fresh carbon dioxide for
further removal of leached, waste, solvent, by-product, or excess base
materials from said vessel and said article upon subsequent removal of
said purge CO.sub.2 from said vessel.
13. The process of claim 1 wherein the pressure vessel is slowly
depressurized after said treatment period to separate essentially all of
said CO.sub.2 from said transport medium.
14. The process of claim 12 wherein the purge CO.sub.2 is entered under
pressure into the pressure vessel above the liquid level of the transport
medium therein, and whereby said medium is forced by said purge CO.sub.2
out of the vessel against a lower pressure head.
15. The process of claim 3 wherein said base material comprises one or more
compounds of the formulae M(OR).sub.n, M(OCOR).sub.n or M(OCOOR).sub.n
wherein M is the cation of a metal selected from magnesium, alkaline earth
metals or alkali metals, n is the valence of M, R is alkyl of 1-20
carbons, or R is an ether group of the formula R (OR).sub.n, wherein R is
hydrocarbon of 1-6 carbons and n is 1-100.
Description
DEAClDlFlCATlON PROCESS
This invention concerns the deacidification of paper products and in
particular paper products which tend to undergo gradual deterioration due
to the influence of acidic materials which may be residual from the
processes of paper making or derived, for example, from the atmosphere.
Such paper articles include books particularly older library books and
other paper products made primarily of cellulosic material.
Much of the paper employed in books is or was prepared by a variety of
processes, nearly all of which employ chemicals which can provide the
production over extended periods of time of acidic anions, particularly
sulfate ions SO.sub.4 =in amounts in the paper which are deleterious to
the cellulosic paper structure. Acidic materials which are present in the
atmosphere, or which may be present from the paper making process or in
various additives or processing aids in paper making, or which are present
in cellulosic material naturally such as the acidic phenolic units of
lignin, also contribute to the paper acidity and its eventual
deterioration. The circumstance of this acidic deterioration is of course
widely known in paper making technology and are particularly troublesome
to archives and libraries and to those collectors or museums who store
valuable literary or other works which can be subject to the problem of
deterioration. Many accountings of the acid catalyzed or promoted
destruction of the cellulose or .beta.-cellulose moities, and various
chemical processes for deacidifying books and the like are found in the
literature such as the U.S. patents identified hereinafter.
It is known in the art of deacidification that various basic materials may
be deposited as fine particles from various organic solvent systems. Such
procedures are described, for example, in U.S. Pat. Nos. 3,676,182;
4,318,963; and 3,939,091, the disclosures of which are incorporated herein
by reference. Also known from such patents is the formation in situ, or
the direct use, of the carbonate or bicarbonate salts, e.g., of magnesium
or organic-Mg compounds such as lower alkoxides, which salts, upon
hydrolysis and ionization occurring over long periods of time in the often
minuscule amounts of water present in the paper will provide neutralizing
hydroxyl ions in sufficient quantity to potentially inhibit acid promoted
deterioration.
Such deacidification chemistry however, is much easier to comprehend than
to apply in any practical and effective manner to tightly bound volumes of
any substantial thickness. In this regard, the processes exemplified in
such patents as cited above may be effective for single sheets or even
books so long as they are loosely bound or the pages are clearly exposed
to the treating solution. Unfortunately, it has become necessary to
deacidify a great number of large books or volumes wherein the pages
cannot be readily presented to the treating solution, for example, where
the books are essentially stacked in large numbers in the treatment
apparatus.
Inherent in these processes also are problems such as chemical attack by
the process chemicals used. For example, it is possible for there to be
solvent leaching of inks or the like, solvation of binding glues, or
deterioration of the binding materials used. This is particularly acute
where alcohol containing solvents are employed. It is likewise a problem
to rid the books or other articles of odiferous solvents, giving the
collection of treated books an objectionable odor. These problems are
especially prevalent where solvents such as petroleum distillates or more
exotic organic materials are employed in essentially undiluted form.
Further, it is also a problem where solvents which have relatively low
volatilities are used as they tend to leave substantial residue films on
the pages.
The present invention has as its objects therefore: to provide a process
for deacidifying books and the like wherein the basic treating materials
penetrate even tightly closed volumes; to further provide process whereby
solvent odor and residue are substantially reduced or avoided; to still
further provide a process which can be carried out in a relatively
inexpensive manner with relatively inexpensive equipment and materials;
and to provide a process which can accommodate simultaneously a large
number of books while still providing an effective distribution of base or
basic or acid neutralizing materials throughout their pages.
The foregoing and still further objects have been, and can be attained, in
accordance with the present invention which is defined in its broad sense
as a process for treating a printed cellulosic article for inhibiting acid
promoted deterioration thereof, comprising in one embodiment the steps of
providing in a closed vessel containing said article, a transport medium
containing carbon dioxide, and a basic or acid neutralizing material
dispersed in said medium to be transported to said article, said vessel
being in one embodiment pressurized with said carbon dioxide at a pressure
of from between about 400 and about 1200 psi, such that at least some of
the carbon dioxide is either in the liquid state or dissolved in the
transport medium, and maintaining said vessel at said pressure for a
sufficient period of time so that the article is substantially pervaded
with said basic or acid neutralizing material. The pressure is then
reduced and the medium separated from said article in a manner that
permits the deposition of said basic or acid neutralizing material in said
article.
In certain preferred embodiments of the present invention: the following
conditions are maintained to achieve the advantages described herein.
The temperature of said medium is maintained below about 31.0.degree. C.
and the pressure is maintained below about 1,100 psi.
The basic material employed can be selected form inorganic and organic
salts, oxides, alkoxides or hydroxides of magnesium, alkaline earth metals
or alkali metals, or mixtures or complexes thereof.
A cosolvent can be admixed with said carbon dioxide in a liquid volumetric
ratio of CO.sub.2 /cosolvent of from about 20/1 to about 1/3;
In practice, using the above conditions, the base material is converted in
situ to a carbonate which, in an aqueous system, gives a basic pH; and
Preferably said vessel and article are flushed during or after said
treatment period with fresh carbon dioxide not containing the neutralizing
compounds.
Further preferred materials, components and techniques are set forth
hereinafter and in the claims appended hereto.
In the operation of this process the article such as books, pamphlets,
newspapers, magazines, technical or historical documents, or the like are
first placed in a pressure vessel of any convenient size, varying, for
example from two liters up to several hundred liters. The article is
preferably supported within the vessel such that at least most of its
surface portions will be exposed. The carbon dioxide of the transport
medium may be fed to the vessel as a gas and pressurized therein to
operating pressure as a liquid depending upon the temperature and
pressures employed. For example, the temperature may be maintained fairly
close to the critical temperature of CO.sub.2, i.e., 31.1.degree. C., and
at pressures such as 650-900 psi, at which the medium will likely be in
the form of a liquid/gas type bi-phase dispersion. For most applications,
the near critical operating mode is preferred for a wide variety of
reasons. Where CO.sub.2 is the only component of the transport medium, it
is preferable to admix the base material with the CO.sub.2 liquid as it is
being fed to the vessel, however, the admixing may be done beforehand or
even within the vessel by any suitable mixing technique. For example, the
base material whether it be solid particulate or liquid may be first
loaded into the vessel and the CO.sub.2 feed gas or liquid passed
therethrough at a sufficient rate and agitation to disperse the base
material in the CO.sub.2 for proper transport to the article and
penetration and/or diffusion thereinto.
The present invention utilizes any of a great variety of base or
neutralizing compositions or base forming materials, all hereinafter being
referred to as base or basic materials, including but by no means limited
to metal hydroxides, oxides, alkoxides, and organic carboxylates,
carbonates or chelates. The useful organic moities of such materials are
essentially limitless in variety. Especially useful organic compounds, for
example, are those of the formulae (R--c--o).sub.n M, (R--o--c--o).sub.n M
and (R--O).sub.n M, wherein R is alkyl group of 1-20 carbons, preferably
1-6 carbons, or R is an ether group of the formula R (OR).sub.n, wherein R
is hydrocarbon of 1-6 carbons, n is the valence of M, and n is 1-100,
preferably 2-40, and most preferably 3-20. The selection of the base
material is made, for example, on its solubility or dispersibility in
CO.sub.2 or in desirable cosolvents, and on its capacity to deliver the
base metal in an oxidized state for easy conversion to the hydroxide or to
a buffer material such as a carbonate which upon hydrolysis yield net
hydroxyl ions in the paper.
As indicated above, the CO.sub.2 may be used with other transport
materials, termed herein as cosolvents, whether they function in all
instances to solvate or not, but which can assist by solvation or
otherwise to disperse the base material in the transport medium. The
cosolvents are, for example, normally liquid hydrocarbons such as hexane,
halogenated hydrocarbons such as the Freon type materials typified by
dichlorodifluoromethane, alcohols such as methanol, and other more complex
organic materials such as hydroxymethylcellulose. The cosolvents are
preferably used in minor quantities and preferably are selected to have
substantial volatilities and little odor such that their residues in the
paper are minimized and inoffensive. It is particularly noted that whether
these cosolvents actually solvate the base material and form a solution
thereof, or merely assist in some manner to disperse the base material in
the transport medium, the high pressure ubiquitous CO.sub.2 presents an
irresistible driving force for transporting or penetrating the base
material as solution or particles into the bound volumes or other
articles.
It is preferred that the cosolvent be soluble or miscible with CO.sub.2
such that a more homogeneous system can be achieved, and also such that
flushing of the vessel with CO.sub.2 after initial removal of the original
transport medium will remove residual cosolvent from the article and
further minimize objectionable solvent odor and residue. In this regard,
in one embodiment of the present invention, a double cell apparatus is
employed wherein the transport medium is expanded with CO.sub.2 to the
working composition in a lower cell and is drawn into a upper cell at
uniform composition until the pressure of the CO.sub.2 is changed. This
arrangement also allows the medium to be returned to the lower cell and
the books in the upper cell to be flushed with CO.sub.2 to remove the
solvent before the cell is opened. Such an arrangement is particularly
desirable where recovery of the medium components is important.
The following deacidification examples or runs will further illustrate
practice of the present invention. Employed in these examples was a
cylindrical steel pressure cell or vessel of about 3.25 inch diameter,
about 21 inches deep, and sealed with a steel lid secured by a threaded
and bolted cap bearing on the lid. The working volume of this cell was
approximately 2600cc and for each run, methyl magnesium oxide (MMO) in
approximately one liter of cosolvent was employed, of the following
composition:
______________________________________
90 ml. MMO concentrate - 10% Mg in MeOH;
60 ml. MeOH alcohol;
850 ml. Freon 113;
938 ml. of solvent containing 1% Mg calculated as the
metal.
______________________________________
In order to fit the cell, the books had to pass through a 3" circle.
Normal-sized books were cut on a paper cutting guillotine to approximately
three inches wide and three inches in height. The books were of two types:
old books discarded by the Killam library and recently-published Harlequin
paperbacks published by Harlequin Enterprises Ltd., Toronto ONT. In 1985.
The reject books were usually discarded because the bindings and paper had
deteriorated to the point that the cost of repair was considered to be
greater than the value of the book. They were printed on average about the
year 1900. The paper showed a strong acidic reaction when tested with
chlorophenol red indicator. The bindings of the Harlequin books were
adhesive applied to single sheets, so-called "perfect" binding. The covers
were printed in bright colours and covered with a sheet of laminated
plastic. The older books showed conventional sewn and animal glue
construction, one book had half-leather binding, one had glazed paper and
most had library classification labels attached to the spine. In Table 1,
"New" refers to the Harlequin paperbacks and "Old" to those from the
Killam Library. To support the books in the cell, two eight-inch pipe
nipples (3/4) were placed in the cell to provide a platform above the
initial liquid cosolvent level on which the books were placed.
It had previously been determined, using smaller cell with glass sight
windows that the volume would expand to about 2000 ml at 700 psi of carbon
dioxide and that at 750 psi and a volume of 2300 ml, a cloud of
methylmagnesium carbonate (MMC) would form.
In a typical run, the books were placed on the platform in the cell just
above the cosolvent system therein, the cell closed and the CO.sub.2 run
in at the bottom of the cell to the pressure required. In the first run
shown below, for example, a pressure of 700 psi was held for 30 seconds,
the pressure then increased to 900 psi to form a cloud, this pressure then
held for 10 seconds and a valve at the top of the cell then opened to
slowly reduce the pressure. The time taken to reduce the pressure from 900
psi varied from 8 minutes to 2 minutes in the various runs. At room
pressure, the volume of solvent returned to a value slightly less than the
original, due to losses in the books and in the escaping CO.sub.2 gas. On
opening the cell, the books were found to be wet with solvent but they
dried off rapidly. The books were separated into two halves, pages from
the front, middle and back were removed and the ink marks examined. The
removed pages were sprayed with indicator and photographed in colour to
record the penetration of the neutralizing solution.
Eight experimental runs were thusly made in the cell and the results are
tabulated in the following table.
TABLE l
______________________________________
Run
# Solution Books Time/pressure
Results
______________________________________
1 90 ml. MMO Dry 700 psi-30 sec.
New-partly wet
60 ml. CH3OH
#20 900 psi-10 sec.
alk in half
850 ml. 113 #7 let down 8 min.
Old alk wetted
2 same as 1 Not 700 psi-8 min.
New-alkaline
book support
dry Old-patchy
lowered #21
#4 let down 8 min.
3 same as Dry 900 psi-8 min.
New-alkaline
1 & 2 #23 Old-patchy
#4 slow let down
clouded?
4 Fresh sol. Not 700 psi-18 min.
New-alkaline
as in run 1 dried Old-poor
#34 900 psi-1 min.
penetration
#8 slow let down
5 As in run 4 Dry 700 psi-8 min.
New-alkaline
#22 900 psi-1 min.
Old-poor
let down 5 min.
penetration
6 As in run 4 Not 700 psi-8 min.
New-alkaline
dried Old-patchy
# 13 900 psi-1 min.
in center
let down 4 min.
7 As in run 4 Not 700 psi-16 min.
Severe damage
dried to laminate
#12 900 psi-1 min.
cover & labels
#33 let down 2 min.
8 HMC-200 cc Dry 550 psi-8 min.
New-alkaline
Fr. 113 600 cc
#24 750 psi-2 min.
Old-good
#6 let down 2 min.
penetration
______________________________________
It is evident that the solution leaches adhesives and coloured inks from
the paper and especially from the coloured printing on the cover of the
Harlequins. The solution took on a dirty brown colour which transferred to
the pages of the books. If the books had been flushed with CO.sub.2 while
still in the cell, they would have come out drier and probably much of the
discolouration of the pages would have been avoided.
As there were only about three liters of Freon 113 available, the solution
was reused for several runs. This made comparison of results difficult,
especially on such questions as the effect of drying the books to remove
moisture. Solutions used with normal books having about 8% water, may have
picked up much of this water possibly making the solvent action more
aggressive. The books were restrained with elastic bands to simulate
closely packed books. Penetration was a problem, and for this reason in
later runs the times and pressures were increased to effect better
penetration. As the treatment time increased, however, the leaching
increased. At 16 minutes treatment at 700 psi and 6 minutes at 900 psi
severe effects on the lamination of the covers, the coloured inks and
spine labels resulted. This suggested that a treatment time of about 8
minutes with this solvent mix and this temperature was the maximum that
could be tolerated. It is likely that fast let down of pressure increases
the probability of delamination.
The best results were reported for run 8 which contained, in addition to
MMC, carboxy methyl cellulose which had been modified to make it more
soluble in methanol. In this run, a pressure of 550psi was held for 8
minutes, followed by 900 psi for 2 minutes. The penetration and buffer
content showed the best results of any of the eight runs. This run used
fresh transport medium and dried books.
In practicing the present invention according to one particularly
innovative and effective technique, the base material, e.g., methyl
magnesium oxide (MMO) in methanol and Freon or other solvent therefor, is
converted to methyl magnesium carbonate (MMC) in the pressure cell. As the
pressure therein is increased to about 750 psi, MMC tends to be released
from the liquid body and form a cloud above the liquid. In instances where
actual contact of the article with the concentrated liquid transport
medium is preferably to be avoided, the article can be so placed in the
cell as to be contacted substantially only by the MMC cloud.
As previously described the most preferred embodiments of the present
invention utilize organometallic dialkoxides of magnesium which are
capable of being solubilized in the selected transport medium and are
converted to the carbonate or oxide or hydroxide in situ in the cellulosic
web of the book or other article. Exemplary values obtained indicating
deacidification potential for such materials showed improvements ranging
from an original pH of 4.5 going to 8.3 in predried books and 8.5 in
off-the-shelf books. The strength of the paper in a known test for fold
breakage rose typically from a value of about 3 for untreated paper to
between 21 to 33 for treated paper.
The following Table shows a summary of results using different transport
media at different pressure conditions. The listing of values for
MgCO.sub.3 is in milligrams of MgCO.sub.3 per square cm of paper surface
tested in four quadrants of the test piece the upper left being (1) upper
right (2) lower left (3) and lower right (4).
TABLE II
__________________________________________________________________________
Sample
Description
Composition
MgCo.sub.3 Content
Finished pH
Fold Breakage Test
__________________________________________________________________________
1) Untreated
NA None 4.5 3
Book
2) Predried
10% Perchloroethy-
(1) 1.05
8.3 21
Book lene CO.sub.2 expanded
(2) 1.40
to 65 psi-10 min.
(3) 0.91
(4) 1.12
3) Ambient Book
10% PCE or TCE-
(2) 1.54
8.5 7
(off-the-
(perchloroethylene/
(3) 1.47
shelf) tetrachloroethylene)
CO.sub.2 expanded to
650 psi-10 min.
4) Ambient Book
10% Freon TF
(1) 2.87
9.1 30
(off-the-
No Pressure-
(3) 2.83
shelf) 10 min.
5) Untreated
100% Freon TF
None NA NA
Paperback
No Pressure
10 min.
__________________________________________________________________________
In each instance the composition of choice was Magnesium Butoxy
triglycolate represented by the general Formula (1):
(C.sub.4 H.sub.9 (OCH.sub.2 CH.sub.2).sub.n O).sub.2 Mg (1)
Other alkoxides which are not volatile under the conditions selected and
which exhibit the necessary solubility in the transport solvent can of
course be employed to advantage.
It can also be seen that the most preferred transport solvent is Freon TF
or Freon 113 which is trichlorotrifluoro ethane which has the advantage of
being able to be used in apparatus which does not need to be pressurized.
In this manner it is possible to employ commercially available equipment
currently employed for dry cleaning establishments and the like without
excessive or expensive modifications to accomplish the objectives of the
present invention.
The invention has been described in detail with particular reference to
preferred embodiments thereof, but it will be understood that variations
and modifications will be effected within the spirit and scope of the
invention.
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